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How does LASIK eye surgery work?

Medicine & HealthLesson on requestFree to read

Quick answer

LASIK corrects focus by permanently changing the shape of the cornea. A thin flap is cut and lifted, then an excimer laser removes microscopic amounts of corneal tissue to flatten or steepen the curve. When the flap is replaced, light bends to land precisely on the retina, so distant objects appear sharp without glasses.

LASIK reshapes the cornea, the eye's clear front window, so that light focuses sharply on the retina instead of slightly in front of or behind it. A surgeon cuts a thin flap in the cornea, lifts it, and removes microscopic amounts of tissue with a cool ultraviolet laser before laying the flap back.

Step by step

  1. Numbing drops are placed in the eye and an instrument holds the eyelids open.
  2. A suction ring steadies the eye while a microkeratome blade or laser creates a thin hinged flap.
  3. The flap is folded back to reveal the stroma, the cornea's middle layer.
  4. An excimer laser removes a calculated pattern of tissue, reshaping the corneal curve.
  5. The flap is smoothed back into position, where it sticks naturally without stitches.
  6. Healing begins immediately, and vision usually clears within a day or two.

Key things to understand

  1. Vision blurs when the cornea's curve bends light to the wrong point, a mismatch called a refractive error.
  2. The surgeon first creates a hinged flap in the top layer of the cornea, either with a blade or a laser.
  3. Lifting the flap exposes the stroma, the thick middle layer of the cornea that gives it most of its shape.
  4. An excimer laser then vaporises precise microscopic amounts of stroma, flattening or steepening the curve.
  5. The flap is folded back into place, heals without stitches, and the new corneal shape focuses light on the retina.

Labelled diagram

  1. Cornea

    The clear front surface that bends incoming light.

  2. Flap cut

    A thin hinged layer is created and lifted aside.

  3. Stroma exposed

    The middle layer that gives the cornea its curve.

  4. Laser reshaping

    Excimer laser removes microscopic tissue in a set pattern.

  5. Flap replaced

    The flap is smoothed back and heals without stitches.

  6. Light focused

    The new curve sends light precisely onto the retina.

How LASIK reshapes the cornea

Real-world examples

  • A short-sighted person who cannot read a bus number across the street may see it clearly the next morning.
  • A pilot or soldier whose glasses would fog or interfere may choose LASIK to meet vision requirements.
  • A person with astigmatism, where the cornea is shaped more like a rugby ball than a football, can have it rounded.
  • Surgeons in India and worldwide perform the procedure as day surgery, with the patient awake and walking out afterwards.

Common mistake

✗ Myth: LASIK burns the eye with a hot laser.

✓ Fact: The excimer laser uses cool ultraviolet light that breaks molecular bonds rather than heat, so it vaporises tissue without burning. Each pulse removes only a tiny fraction of a micrometre of cornea.

People also ask

How does laser eye surgery actually fix your vision?
The cornea does most of the eye's focusing. If its curve is too steep, light focuses in front of the retina, causing short sight; too flat, and light focuses behind, causing long sight. LASIK removes tiny amounts of corneal tissue to change that curve so light lands exactly on the retina.
What happens during LASIK step by step?
The eye is numbed, then a thin flap is cut in the cornea and folded back. An excimer laser removes a computer-calculated pattern of tissue from the exposed middle layer, reshaping the curve. The flap is laid back in place, heals on its own, and vision usually clears within a day.
Is LASIK permanent or does it wear off?
The corneal reshaping itself is permanent because removed tissue does not grow back. However, the eye keeps changing with age, especially near vision after forty, so some people still need reading glasses later. Vision can also drift slightly over the years, and a few people choose a second treatment.
Is LASIK painful?
Most people feel pressure but little pain during the procedure because numbing drops are used. Afterwards, a gritty or burning sensation is common for a few hours. Any severe or worsening pain should be checked by a doctor.
How long does it take to recover?
Vision often improves within a day, though it can fluctuate for weeks as the cornea settles. Many people return to work within a few days. Final stable vision typically takes a few months.
Can the effect wear off?
The reshaped cornea is permanent, but eyes continue to change with age, so vision can drift over years. Reading vision especially declines in the forties, a change called presbyopia that LASIK does not prevent. Some people later need glasses again.
Who is not a good candidate?
People with very thin corneas, unstable vision, severe dry eye, or certain autoimmune and eye diseases may be advised against it. A thorough eye examination is needed to judge suitability. Pregnant or breastfeeding women are usually asked to wait.

Part of the guide: How Your Body Works →